Insect Pests of Textiles

'Ragged Edge'

David Pinniger

Insects
have been known to damage textiles from earliest times, as illustrated
by the biblical reference, 'Your clothes are moth eaten',
James 5.2 and Aristophanes' immortal report 'Moths were eating
the feather plumes of helmets' in 400 BC.

Although
modern methods of chemical and environmental control have reduced
the incidence of pests there is still need for vigilance to ensure
that insects are not allowed to breed and damage fabrics and textiles.
Carpets, curtains, upholstered furniture and other objects which
are most susceptible to attack contain material of animal origin
including wool and wool products such as felt, natural animal fur,
feathers and hair, and untanned leather and skins.

Although
silk can be attacked, serious damage usually only occurs when objects
are soiled. Insects will not breed in cotton and so it is not usually
damaged although some insects will chew exit holes through cotton
covers. Damage to covers can be a particular problem with cushions
and upholstery filled with feathers or hair.

The
main insect pest species in Great Britain are clothes moths and
carpet beetles which are very different in both their appearance
and the damage which they cause.

CARPET
BEETLES

Figure
1: Adult carpet beetle Anthrenus verbasci on hogweed flower

Figure
2: Woolly bear larvae of the carpet beetle Anthrenus verbasci

The
most common species is the varied carpet beetle Anthrenus verbasci,
although there are a number of other species of Anthrenus which
are similar in appearance and habits including the Guernsey carpet
beetle Anthrenus sarnicus, which is now well established in London
and causing increasing problems. Adult Anthrenus are small rounded
beetles, 23mm long, covered with patterns of grey and gold scales
(Figure 1). Adult beetles fly outdoors in late spring and early
summer where they mate on flowers before returning indoors and may
frequently be found on window sills. The damage is not caused by
the adult beetles but by active, short, fat, hairy larvae often
referred to as 'woolly bears' (Figure 2). These larvae are voracious
feeders and will rapidly demolish fur, feathers and woollen textiles.
As they grow they moult and leave empty cast skins which may be
the first signs of beetle attack. Carpet beetles can be found in
natural situations such as birds' nests and in some houses they
have a direct route into the premises from birds' nests in attics
and chimneys.

CLOTHES
MOTHS

Two
species of moth will attack and damage textiles - the case-bearing
clothes moth, Tinea pellionella, and the common or webbing clothes
moth, Tineola bisselliella. The adults are small, dull, grey-fawn
moths 5-7 mm long, which scuttle around rather than fly and when
at rest fold their wings along their back. Moths hide in dark areas,
shun the light and lay batches of eggs on fur, feathers, skins,
wool or soiled silk. The larvae which hatch from the eggs spin silk
webbing. The case-bearing clothes moth larva, Tinea, spins a cocoon
around itself leaving the front end open so that it can use its
jaws and legs (Figure 3). It then eats as it crosses the material
carrying its case and leaving a trail of grazed textile or fur with
some fragments of excreta or 'frass'. The larva moults within the
case and when fully grown it pupates within the cocoon. Eventually
the adult moth emerges to mate and lay eggs.

The
common or webbing clothes moth, Tineola, has different habits; although
the larva also spins silk it leaves this as a tunnel or sheet of
webbing across the attacked material under which it grazes. Damage
by this species is accompanied by copious webbing tubes or sheets
which frequently include large amounts of frass, and infestations
appear far more 'messy' than the damage caused by Tinea. Adult moths
can fly in through windows or open doors and can also originate
from birds' nests. One generation normally takes a year but development
can be rapid if local conditions are suitable. Damage is also more
concentrated in dark areas and crevices or creases, for example
under furniture and cushions or where carpets or textiles are folded.

The
pelleted excreta or frass produced by the larvae of clothes moths
is frequently mistaken for moth eggs. However, frass pellets are
hard and opaque whereas moth eggs are very small and translucent
and vulnerable to physical damage. Contrary to popular opinion,
eggs will not remain dormant in textiles and then hatch many months
later.

GENERAL
DETRITUS FEEDERS, MOULD FEEDERS AND SCAVENGERS

There
are very many insect types and species in this group including the
Australian spider beetle Ptinus tectus, booklice Liposcelis bostrychophilus
and silverfish Lepisma saccharina. These insects generally cause
only nuisance and low levels of damage but occasionally localised,
humid environmental conditions encourage insect populations to build
up to levels sufficient to cause serious damage.

WHERE
DO INSECTS COME FROM?

Insects
cannot be spontaneously generated in objects and it follows that,
if infestation develops it must have been acquired from some other
source. The most obvious way for insects to gain access to houses
is through doors and windows from the outside world. Carpet beetles
fly readily in warm summer months and even one fertilised female
can lay sufficient eggs to start an infestation. In general, the
warmer the weather, the greater the risk from invasion. Birds' nests
and dead animals in attics are the natural home of many pests where
they live quite happily on feathers, hairs and excreta. When insect
numbers exceed the food available they will spread out in search
of other breeding sites in the house. Some pests will live in a
house for many years at low levels without apparently causing a
problem and it is not until all the conditions are right that serious
damage occurs.

PEST
PREVENTION

A
successful strategy for pest prevention depends upon the integration
of inspection, exclusion and environmental control. Good cleaning
standards are essential because pests thrive in a dirty, undisturbed
environment. Debris and rubbish provide shelter from detection as
well as food. With regard to the building environment there should
be no compromise; all areas should be kept as clean as possible.

Insects
can be introduced on objects and textiles which are already infested
and if the insects remain undetected then a serious problem may
develop. Visual inspection supplemented by the use of sticky monitoring
traps will provide early warning of insect presence and may allow
a potential problem to be identified before serious damage can occur.

CONTROL

What happens when insects are found? A panic-stricken grab for the
nearest can of insecticide is not the answer. A rational and carefully
considered reaction is required when the following questions are
answered:

Is
the insect a pest or a non-pest?

Is
the insect alive or dead?

Are
there many insects or very few?

Are
the insects widespread or restricted to one area or object?

Is
there damage to objects?

Are
there other objects at risk in the area?

Can
the object or area be isolated or removed?

If
it is decided that control measures must be applied then it is important
to choose the most appropriate course. Effective control of the
insects can be achieved in a number of ways including physical and
chemical methods.

Selective
application of the correct insecticide formulation to potential
breeding sites in the building may be useful but most residual and
aerosol insecticides which are sold for use in household situations
are rarely effective or appropriate for use on infested objects.
If inspection of objects shows that remedial treatment is necessary
to control infestation then it is important to consider the range
of options which are now available. These include fumigation treatment
with a gas such as the insecticide methyl bromide, or the atmospheric
gases carbon dioxide or nitrogen. In most cases such treatment will
have to be carried out either off-site in a special chamber or on-site
in a bag or 'bubble' enclosure. It is also possible to kill insects
with extremes of temperature under controlled conditions which avoid
damage to objects. The use of a freezer to reduce temperatures to
-30°C has been successfully used to treat textiles but it requires
a very careful regime of handling and enclosing objects in bags.
High temperatures of 55°C can also be used to kill insects when
combined with close control of humidity as used in the Thermo Lignum
treatment.

The
choice of the most appropriate and correct response will depend
upon a number of factors and it is usually advisable to get expert
advice. This may not only prevent further damage but also may avoid
unnecessary and expensive remedial treatments.

This article is reproduced fromThe Building Conservation Directory, 1996

Author

DAVID PINNIGER
is a research etymologist at the Ministry of Agriculture Central
Science Laboratory in Slough. He is the pest detection and control
consultant for a number of UK museums and is a specialist lecturer
for insect bio-deterioration courses including the ICCROM courses
Scientific Principles of Conservation in Rome and Paper Conservation
in Austria.